Rotary compressor



June 1, 1965 R. E. LAMBERTON ETAL 3,

ROTARY COMPRESSOR 3 Sheets-Sheet 1 Filed Oct. 3, 1963 INVENTORS RALPHE LAMBERTO/V ORV/LLE'R LOWTHER BY ROBERTA. REED/N6 June 1965 R. E. LAMBERTON ETAL 3,186,631

I ROTARY COMPRESSOR Filed Oct; 3, 1963 3 Sheets-Sheet 2 VI LE R. BY ROBERT A. REDD/NG MAHONEY, MILLER GRAMBO Arrow/52's June 1, 1965 R. E. LAMBERTON ETAL 3,136,631

ROTARY COMPRESSOR Filed Oct. 3, 1963 5 Sheets-Sheet 3 INVENTORS RALPH E LAMBERTON ORV/LLE R. LOWTHER BY ROBERTA. REDD/NG MAHO/VE Y, MILLER 8RAMBO Z/MJKM ATTORNEYS United States Patent 3,186,631 ROTARY COMPRESSOR Ralph E. Lamberton, Worthington, and Orville R. Lowther and Robert A. Redding, Columbus, Ohio, assignors to The Jaeger Machine Company, Columbus, Ohio, a corporation of Ohio Filed Oct. 3, 1963, Ser. No. 313,601 19 Claims. (Cl. 230-46) Our invention relates to a rotary compressor. It deals, more specifically, with an unloading'system for a rotary compressor whereby the power required to drive the compressor while it is running in an unloaded state is greatly reduced as compared to power requirements of prior art compressors now commonly in use in a similar state.

This invention deals mainly with compressors of the internally oil-cooled, sliding-vane rotor, positive-displacement type. It is applicable, particularly, to a rotary compressor of this general type which is driven by an electric motor although it is not necessarily limited to an electrically-driven compressor.

At the present time, compressors of the general type indicated are provided with unloading systems but by these systems only the intake valve of the compressor is closed so that atmospheric air to be compressed will not be taken into the compressor and a very high vacuum will result at the intake side of the compressor unit. The rotor continues to rotate in the unloaded state of the compressor, even if there is no need to compress air, to provide for proper circulation of the lubricant-cooling oil in the system. However, even in the unloaded state, the rotor is working against the pressure in the air receiver which is reflected back to the discharge chamber of the high-pressure cylinder. Since no air is entering the low-pressure cylinder, all sectors of both rotors bounded by the sliding vanes are operating at a partial vacuum. As each sector of the high-pressure rotor is exposed to the receiver backpressure, air expands into this cavity and must be recompressed back to a pressure slightly greater than that of the receiver, as the rotor vanes pass the discharge port. This alternate expansion and recompression results in a high power consumption for driving the rotor in the unloaded state of the compressor as compared to the power consumption required to drive it in the loaded state of the compressor, ordinarily amounting to about 75% of the energy required to drive it in the loaded state. This is particularly true of the electrically-driven compressors in which the electric motor drives at constant speed. Even in connection with rotary compressors driven by internal combustion engines, where the throttle is moved to a minimum speed position during the time the compressor is unloaded, a substantial amount of power and, therefore, fuel 'is required to drive the rotor while the compressor is unloaded.

It is the main object of this invention to provide an unloading system for a compressor of the type indicated which may be termed a free unloading system in that the rotor will not be required towork against the pressure of the compressed air in the receiver part of the compressor unit and, therefore, the amount of power required to drive the rotor during that unloaded state will be a minimum. f

Another object of our invention is to provide a freeunloading system of the type indicated in an internally oil-cooled compressor wherein an unloading point in the system is selected where the air is sufficiently tree of circulating lubricating-cooling oil to allow it to be exhausted to the atmosphere without excessive loss of oil.

Another object of our invention is to provide a freeunloading system of the type indicated by which theunloading of the compressor is accomplished without ventoil in the manifold 14L ing substantial amounts of previously-compressed air from the receiver part of the compressor system, such as from the air receiver tank and associated air-oil separator.

A further object of our invention is to provide a control system for a compressor of the type indicated which preferably will automatically control starting and stopping of the compressor as well as loading and unloading of the compressor in accordance with our invention.

A further object of our invention is to provide a freeunloading system of the multi-stage type wherein an interstage manifold connects the stages of the compressor having an oil-scavenging system associated therewith for preventing the accumulation of excessive amounts of oil in the manifold while the compressor is operating in the unloaded state.

Various other objects will be apparent as this description progresses.

In the accompanying drawings, we have illustrated one embodiment of our invention, the embodiment shown being a compressor which is electrically driven, but it is to be understood that many specific variationsare possible without departing from basic principles of our invention.

In these drawings:

FIGURE 1 is a schematic diagram of the fluid system of a rotary compressor embodying our invention with certain electrical members indicated in association therewith.

FIGURE 2 is a schematic diagram of the electrical system used on the compressor in accordance with our invention.

FIGURE 3 is a schematic sectional view illustrating details of the oil-scavenging system associated with the free-unloading system.

With reference to the drawings, in FIGURE 1 we have illustrated schematically a rotary compressor system to which our invention is applicable, but it is to beunderstood that we are not limited to this specific compressor system. The structure of the rotary compressor itself may be generally like that disclosed in the patent to Lamberton No. 2,739,758 issued March 27, 1956, but its drive is shown herein as being an electric motor. The general arrangement and positioning of the various units of the compressor system may be similar to that disclosed in the copending application of Paugh Ser. No. 215,390 filed August 7, 1962.

In FIGURE 1,' we indicate a compressor 10 of the rotary type which is driven by an electric motor indicated at 11. The compressor maybe of the multi-stage type and is shown as having a lowpressure cylinder 12 and a high-pressure cylinder 13. These cylinders are connected together by an interstage manifold 14 so that low-pressure air discharged from the cylinder 12 will be conducted into the cylinder 13 for further compression. The lowpressure cylinder 12 houses a rotor (not shown) preferably of the sliding vane type which is coupled to and is driven by the motor 11. The rotor in the low-pressure cylinder is coupled to and drives the rotor (not shown) which is in the high-pressure cylinder 13. Thelow-- pressure cylinder 12 is provided with an air intake conduit 15 having a two-way unloading valve 16 connected therein which isof the piston type and is adapted to be actuated by air-pressure. A filter 17 is also provided for the intake conduit 15 so that air taken into the low-pressure cylinder 12 from the atmosphere will be filtered. Also connected to the filter 17 is an air conduit 18 which is adapted to ,inspirate air into the interstage manifold 14, to the low-pressure end of which it is connected as shown. This condiut 18 is provided with the check valve 19. The conduit 18 functions in a manner'to be described in detail later to aid in preventing undue accumulation'of V press'or' to the point of use.

leads from the lower portion of the separator 24 and to the air-service conduit 25 which has a check valve 26 1 therein and which supplies the air compressed by the com- An oil bleeder conduit 27 connects to the low-pressure end of the. manifold 14, being provided with a strainer 28 and a check valve 29,

associated with a restricted passage to the manifold, connected therein in series. This conduit functions-to return the separated oil from the separator 24 to the inter-stage manifold during normal loaded operation of the corripres rotor in the cylinder 13. The discharge of this pump is connected by an oil conduit 31 to the oil supply system of the cylinders'lZ and 13 which is indicated schematically asth'e gallery 32 and a flow switch FLS is interposed in this oil conduit 31 although a pressure switch may be used instead of this flow switch. The inlet side of the, pump is connected by an oil conduit 33 to an oil cooler indicated at 34 and a filter 35 is interposed in this conduit. Also, a thermally-actuated switch THl is associated with this conduit. andis'act'uatedby. the temperature of the. oil therein flowing to the pump 33. A blower. isindicated at 36 as part of the oil cooler and is driven by an electric motor 37. An oil conduit 38leads from 2 which may be of thewell known spool type and which is spring offset to a normal position as indicated 'when the solenoid is dee'nergized. I This valve is connected by a conduit 45 to a conduit 48 through an air-liquid separator 41 and'conduit 48 is connected to the air-service conduit-25. A restrict0r4 6 is interposed in conduit '25 bel tween check-valve 26. and the separator 24- with the corn 'duit48'connection being'on the high-pressureside to assure fast pressure built-up whenvstarting" for valve operation. A pressure-actuated electrical switch PS is connected to the con'duit48.;

Connected in the 'system is a multi-path, directional flow. control 50, termed herein as a five-way valve, which 1 is'alsopart. of the unloading system according to this Thisvalve may be of therspool type as ilinvention. 7 lustrated which isspring centered and operated by an air actuator, 50a and 50b, provided at each end of the spool. This valve is controlled by the four-wayvalve S2, previously-mentioned, for operating: the system in either-the loaded stateor the unloadedstateu The valve, actuator" sea, utilized foruuloaded operation, isconnectedby cone hit to one port of the four-Way valve 82 through a check valve,51 which is by-passed by a restricted by-pass 52. A solenoidactuated .thre'e-way valve 84 is inter posed in conduit 44 between the air. actuator 56a and the 1 I check valve'51and restriction 52, The other valve acoil conduit 33 leading from 4 tuator 50b is connected to arsecond port of the four-way valve S2 bya conduit 53 whichhas a solenoid actuated three-way valve S3 interposed therein. Valves S3 and S4 may be of the spool type whichare spring. ofiset to a normal position when the solenoid thereof is deenergized. The valve 50 includes three inlet ports, one of which is connected by a conduit 54 tothe discharge conduit'2tl leading from the high-pressure cylinder 13'. A thermallyactuated switch THZ is connectedin the dischargeconduit 20 so as to be affected by the temperature of the compressed air and oil mixture dischargedfromthe high pressure.cylinderwhether the airfand oil mixture flows to the air receiver 21 or to the valve 50. The oil reservoir tank 23jis connected to a second inlet port'of the valve 50 by a conduit55 leading from the lower side orbottor'n of the oil tank. The third inletport ofithe valve 50 is' connecte'dby a conduit 56"tojthe bottom ,or oil outlet-.ofan' air-oil separator57 whichrmaybe ofthejcyclone type. This separator 57 has an air exhaustoutlet at its upper end whichrnay be provided with an exhaust'silencer58. (3f the valves two outlet ports, one is. connected by a conduit 59 to the inlet of the separator 57 and the other is connected by a conduit 60, to the inlet port ofthe by pass valve 40. t

An electrical power and control circuit for operation of the compressor 'in;accordance withthis invention is diagrammatically illustrated in FIGURE-2. .The control circuit, as illustrated, is adapted to not only automatically control'operation of the compressoras to loaded and unloaded operation in accordance with service 'demands'but to automatically start and stop the apparatus in ace-orda'nce withpredetermined,operational conditions. It is the 1 primary'functionot the control circuit to automatically operate the several components of the apparatus as to providetor free-unloaded operation of the compressor.

The electrical power circuit is connected to a threephase, alternating current power distribution system of suitable voltage and includes the threepower lines L1, L2 and L3. A three-pole disconnect switch l'is interposed in the;.power'lines along with the customary overcurrent protective devices such as the. fuses 61d. Con.-

nected to the power'linesLl, L2 and L3jare the electric motors 37 and 111, previouslyieferred to, foroprati'ng the oil cooler blower .36 and driving the rotary compressor 16'. Each respective niotorll and 37 is connected to the power lines through a magnetic contactor of thetype having a set of normally opencontacts, ICR-it, {CR2 and TOR? and Z CRI, zcazand ZGRS, controlled bytheir respective electromagnetic solenoids, or=operating coils 'ICR and. 2CR.- Also incorporated. in each magnetic c'ontactor are the usual overload Iprot'ectivedevices consisting of the associated thenrn'ally res ponsivei elements. and normally closed contacts oLr, :oL2, 0m and otsf-As-wiu be noted from the 'circuit'diag'ra'm, theoverload devices 0L1 and 0L2 are associated with the compressor motor 11 normally closed while the start switch .63 :is normally open with the cont-acts of each being'seriallyfconnected across the secondary output conductors of thetransforiner 62. Also connected in series wanna: switches 63 and p 64 is the coil SCRJof a circuit-maintaining 'r elayfwhich is operable to-by-pa ss the start switch 63, once the compressor apparatus has been startedand is operatingnormally. Completion of the start-and stopcirouiti's' through the serially-connected contacts of. the't-herfnrostaticallyoperatedfswitch THZ,.previouslymentioned,"and the nor-t rna-lly closed contacts-of the overload devicesOL-l and 0L2 associated with the compressor motor i 11.. The

thermostatic switch THZ is provided with a normally closed contact which will open whenthe temperature of the oil-air mixture discharged from the high-pressure stage 13 of the compressor exceeds a predetermined value. In this present embodiment, the switch THZ is set to open at about 240 F. and will break the startstop circuit, thus protecting the compressor apparatus firom damage due to high temperatures. Serially connecting the contacts of the overload device-s 0L1 and 0L2 in the start-stop circuit provides further protection for the compressor apparatus in the event that an overload should occur in the compressor motor 1-1. An overload of this form would also break the startastop circuit thus deenergizing the control circuit and disconnecting the compressor and blower motors 1'1 and 37 from the power lines L1, L2 and L3.

A holding circuit is connected in shunt relationship with the start-stop circuit which automatically operates to deenergize the control circuit and disconnect the compressor and blower motors 1-1 and 37. This circuit includes the normally open contacts 3CR1, actuated by the relay coil 30R, which .are serially connected with the parallel connected contracts 1TR1 of a time delay relay and the flow switch FLS, previously mentioned, and the operating coil ZTR of a time delay relay connected in series therewith. The contacts 1TR 1 of the time delay relay are normally closed while the contacts of the flow switch FLS are normally open. As previously indicated, the flow switch FLS is interposed in the discharge conduit 31 of the oil pump 30 and is responsive to a minimum desired oil flow necessary for operation of the compressor. The flow switch FLS assures that oil is being continuously pumped into the compressor and operates to deenergize the control circuit at any time the oil flow decreases to such an extent that it is below the minimum.

The coil ZT-R controls the normally open contacts 2TR1 connected in series with the holding relay contacts 30R]. and in shunt relationship to the start switch 63. This time delay relay is of the type wherein the contact action is retarded upon deenergization of the operating coil. Thus, when the start switch 63 is momentarily closed, a circuit is completed throughcontacts lTRl and coil ZTR causing contacts 2TR1 to close instantaneously. With contacts ZTR-1 closed the start switch 63 may be opened and the control circuit will proceed to automatically operate the compressor and blower and other associated apparatus even though a momentary interruption should occur in the holding circuit. Should the circuit including the timer coil ZTR be opened at any subsequent time, such as would result from a momentary fluctuation in the oil flow in conduit 3-1, the contaotsZTRl Will remain closed until expiration of the delay interval. Energization of coil ZTR at anytime including during a timing interval will reset the mechanism for subsequent operations. A delay of approximately five second-s time has been found 'sufficient to prevent intermittent operation of the automatic circuit due to fluctuation of lubricant-cooling oil ilow.

, Connected in the control circuitin dependent relationship to the holding and start-stop circuits are the operating coils 1CR and ZCR for the magnetic motor contactors. Each coil, lCR and 2CR, is connected in series with its respective serially-connected overload contacts, 0L1 and OIJZ, 0L3 and 0L4. The coils ICR and 2CR with their respective overload contacts are connected in shunt relationship and may be connected to the holding circuit through either a manually actuated selector switch 65 or through the normally closed contacts 3TR1 of a time delay relay. .The connection of the operating coils ICE. and R to the holding circuit is made at the juncture of the parallel connected timer contacts 1T R1 and flow switch contact FLS whereby the relay contacts 3CR1 will be etfect-ive to control the operation of the blower and compressor motors 1 1 and 37. The selector switch 65 is of the two-position type and is adapted to complete the circuit to the operating coils 10R and 20R in a first position and is open-circuited in the second. As will be noted from the circuit diagram, the selector switch 65 is connected in shunt relationship to the timer contacts 3TR'1 and is effective to bypass these contacts when in the first position. interposed in the circuit of the operating coil ZCR are the contacts of the thermal switch THl, previously mentioned. These contacts are of the normallyopen type with the switch being set to close the contacts at about 110 F. and to open the contacts at about F. The thermally-responsive element of the switch is installed in the oil cooler outlet conduit 33 and is eifective to maintain the temperature of the oil within predetermined limits by controlling the operation of the oil cooler blower motor 37.

Also connected in shunt relationship to theoperating coils llCR and ZCR is the operating coil ITR of the time delay relay. This relay is of the type wherein the contact action is retarded upon energization of the operating coil. In the present compressor system, it has been determined that a delay of about 10 seconds time in opening of the contacts lTRl is desirable for optimum operation of the system. At any time the coil ITR is deenergized, the coil and contacts lTRl will be instantane ously reset to their normal position.

An automatic free-unloading circuit is provided by this invention to simultaneously open the compressor highpressure stage discharge to the atmosphere, isolate the oil separator and air receiver tanks, and to close the unloader valve 16 preventing further intake of air. The free unloading circuit includes the solenoid-actuated valves S1, S2,, S3, and S4. Selective energization of the solenoids of the valves S1 and S2 is eifected through a pressure switch PS. This switch is responsive to the pressure in the air service conduit 25, through the interconnecting conduit 48, and is of the single pole, double-throw type. In the first or low-pressure position, the pressure switch PS, the pole of which is also connected to the holding circuit so as to be in series with the relay contacts 3CR1, completes a circuit through the solenoid of the valve S1. In the second or high-pressure position, a circuit will be completed through the solenoid of the valve S2, The operating pressure limits of the switch PS, in the present embodiment, are set to maintain a circuit through the solenoid of the valve S1 at any time the pressure in the air service conduit 25 drops below 90 p.s.i.g. and remains below p.s.i.g. and to maintain a circuit through the solenoid of the valve S2 at any time the pressure in the air service conduit reaches 105 p.s.i.g. and remains above 90 p.s.i.g. The solenoids of valves S3 and S4 are connected in parallel with the timer coil 1TR and the operating coils ICR and 20K of the magnetic motor contactors and will be energized at any time the compressor motor is operating.

Connected in parallel with the solenoid of the valve S2 is the operating coil 3TR of the third time delay relay. This relay is operative to efiect automatic start and stop of the compressor and blower motors 11 and 37 in accordance with the air pressure in the air service conduit 25. This relay is also of the type wherein the contact action is retarded upon energization of the operating coil. Since the coil 3TR is connected in parallel with the solenoid of the valve S2, it will be energized simultaneously therewith when the air service conduit pressure reaches 105 p.s.i.g. The contacts 3TR1 will not open, however, until the time delay of the relay has elapsed. At the expiration of the time delay, the contacts 3TR1 will open and deenergize the operating coils lCR-and ZCR causing the blower and compressor motors 37 and 11 to stop and deenergize the solenoids of the exhaust valves S3 and S4. The delay, which may be of the order of 15 minutes, has been found advisable in order that the number of starts will be limited to four in any onehour time interval. This is necessary to prevent overheating of the compressor motor 11 due to the relatively large starting current. When the air service conduit presstream.

sure drops to 90 p.s.i.g.,'thus resetting the pressure switch PS and de'energizing the solenoid of the valve S2, the timer coil ST'R will also be deenergized and will be reset in preparation for another timing interval. ously upon resetting of the operating coil 3TB, the contacts 3TR1 will close, if previously opened, permitting restarting of the compressor and blower motors l1 and 37.

As previously indicated, the conduit leis part of'an oil scavenging system according to our invention which prevents the accumulation of oil in the manifold 14 (Eur-- nstantaneing the unloaded operation of the compressor 14). This system is shown more in detail in FIGURE 3 and functions during the time the compressor is operating inthe freely unloaded state. This scavenging system is an airinspiring system which is connected to the manifold 14 and whichioperates on a pressuretdiiferential between. the manifold and atmospheric air at the compressor intake to draw air from the atmosphere, during the unloaded cycle and to jet it throughthe manifoldin the dl rection of normal flow through the manifold and thereby to "scavenge the oil therefrom. o

The bleed or, drain conduit 27 running from the oil separator 24 functions to return separated oil from the separator24 to the circulatingoil system via the inter? stage manifold 14 during loaded operation of the com-., During load-ed operation, the pressure within pressor.

lated, causes a hydrahlicfiam between the vanes of the high-pressure rotor. Such an accumulation of oil could damage or. distort theyanes. Also, if the air compressor is a. portable compressor and .is' used for work on very V irregular terrain, the compressor may be operating at very steep angles which could possibly cause anexcessive accumulation of oil in the lowest end of the manifold with resulting serious damage or breakageof the vanes of the, rotor, in the high-pressure; cylinder Since during the unloaded state of the compressor there is no substantial flow of air through the manifold 14 from the low-pressure cylinder to the high-pressure cylinder-but on the other hand there is a very low-pressure or vacuum condition in the manifold, which tends to cause accumulation of oil in the manifold, especially atthe downstream end thereof, the jet of; scavenging air created by our scavenging system and acting ,in the same direction as the normalflow through the manifold, will prevent the accumulation of oil therein;

According to our invention,'we provide'the' conduit 13 as a means to prevent accumulation of oil in the interthe interstage manifold 14 will be substantially less than that within the separator 24 thereby assuringreturn of the separated oil to the oil "system. For this purpose, it

is'necessary to select a point of reentry having a lower pressure. a

While the compressor is loaded, the oil passing from the low-pressure cylinder 12 with the air will pass into the high-pressure cylinder 13 and out to the air receiver 21. The compressed air fiowsfrom the receiver 21 into.

the separator 24 and-any. oil vapors remaining in theair are retained in the filtering elements in the oil separator and are passed from the separator into the drain or bleed line 2'7; The check valve 2% in the conduit 27' will pre- 7 nected to the'valve unit ldat the inlet sleeve'lll at a.

ventoil from being forced back up into the separator 'wh'en the compressor is started. As soon, after starting of the compresson'as air pressure in the discharge end of the oil separator 24 exceeds thepressure in the manifold 14, any oil collected by the oil separator 24 will be forced into the manifold 14. Themain stream of oil and air, as indicated, during loaded operation of the compressor will flow through. the manifold 14 and there will be no tendency for oil to accumulate therein at this, 'time' The oil and air returned from the separator 24 b'y'the conduit 27 will merely be added to -that main stage manifold 14 during the periods when the compressor is unloaded. Thisconduit 18 constitutes a piping system, between the interstage manifold ,and'theair intake of the compressor; which provides for the inspiration of air through .the intake filter 17 to the manifold 14'to produce a jet'therein .which will aid in forcing the oil from the manifold into the high-pressure cylinder 13. For this purpose, we connect the conduit 18 at one endto the'unloading valve unit 16 and at' its oth'erend to the upstream end of .the manifold 14. *Thus, the inlet end 72 of the conduit 18, asshown in FIGURE 3,.is conpoint intermediate the filter..17 and the valve .seat 69. The air taken into theconduit 18will, therefore, be filtered air. The other or outlet end 73 of the conduit is connected to the manifold 14 at its upstream end and directly above the bottomof the manifold to direct the air flow parallelto thebottom' wall, as-best shown in FIGURE 3. The outlet end 74 of the bleeder pipe or conduit 27 is also preferably connected'to the manifold Him a similar I manner. The outlet ends 73'and 74 of the conduits 18 The compressor air inlet is controlled bythe valve '16 '7 which may be .a common type of unloading valve, an v example of which is illustrated in FIGURE 3. It comprises a piston type valve member 66 which isactuated by receiver pressure reaching it through the conduits-41,

44, and 4% controlled by the valve S2 previously'men tioned. Thistvalve member 66 is disposed in a housing 68 mounted on the low-pressure cylinder 12 over its inlet 15 and communicating therewith. The housing is pro-.

videdwith an inletsleeve 7d leading-the'reinto having a valve-seat. 69 at its inner end withwhich the valve memher '66 cooperates. On the outer end of the inlet sleeve= 70', the filter unit 17 ismounted. Atmospheric air .will

, be drawn through the filter unit 17 and be filtered before a I it enters thjehousing 63 through the inlet sleeve 7h.

' and 27'are directed toward .the opposite or downstream ing system, there could be a rapid build up of oil in the interstage manifold 14. Since at thistime the manifold 14 is under high vacuum, there is a substantial pressure differential between the manifold and the compressorfilter l7 whichicornmuni'cates with the atmosphere, it being understood thatjthe unloading valve 16 is closed at this time. Also; at this time, as will later appearfthe valve S1 is closed blocking the bleeder conduit 27; The pressure differential between atmosphericv air at the inlet and the low: pressure in the manifoldl l' is utilized "according to our invention, to inspire' atmospheric airiinto said manifold and use it as a scavenger jet to act in a downstream direction on any oil tending to accumulate therein and to cause the. oil to flow toward and into the high-pressure cylinder 13. .This' jet will scavenge fromlthe manifold Without our scavenging system, if the compressor runs for long periods unloaded, an excessive amount'of oil will accumulate in the int'erstage manifold 14. Should there I be a'demand for additional compressed air subsequent toan accumulationof oil in the manifold thus returning anunloaded state, air twill be inspired from the chamber the compressor to loaded operation, .the accumulated oil will. instantly be drawn into the highsprcssu're cylinder 13 and, ifasufficiently large volume-of oil'has accumu any oil which'tends' to accumulate therein during the unloaded operation 'of 'the compressor. r I

'I'hus, 'with thisrarrangemen'tgs'ince thev unloader valve 16 is totally closed When the compressor is running in in the sleeve 76) between'the: valve seat 69 and the intake ,filter 7 Consequently, only filtered'air isdrawn into theinterstage manifold 14 through theconduitls, This inspired air is drawn into the manifold 14 along the bottom thereof thereby aiding in moving oil therein from the low-pressure cylinder discharge to the high-pressure cylinder intake. When the compressor reassumes the pumping load, the valve 16 is opened by atmospheric pressure since holding pressure has been exhausted from the conduit 41, a positive pressure develops in the manifold 14 and the check valve 19 is closed thereby preventing air and oil flow-back through the conduit 18 into the compressor intake. M

The operation of the oil-scavenging system of this invention has been described above in detail. This system will function whenever the compressor is operating unloaded.

The general operation of the compressor and especially as it relates to the free-unloading operation is briefly described herein as related to the schematic diagrams of FIGURES 1 and 2. In these diagrams, the several elements or components are shown in their normal positions as when the compressor system is not operating. In this condition, the disconnect switch 61 will be open and the pressure in the air service conduit 25 may be at atmospheric pressure or at least below the minimum desired operational pressure of the system. The separator oil conduit valve S1 will be closed since its solenoid will be deenergized. Also, the solenoid of the control valve S2 is deenergized and this valve will be positioned as shown to exhaust or vent the conduit 44 to the atmosphere and connect conduit 53 to conduit 45. The solenoids of the exhaust valves S3 and S4 are deenergized and the valves are positioned so as to block conduits 44 and 53 and vent the respective air actuators to the atmosphere through an exhaust port. The directional flow control valve 50 will thus be spring centered with all ports blocked. The unloader valve 16 will thus be in its normally open position as its actuating air cylinder is not pressurized. Since the temperature of the lubricating and cooling oil in the system will be below the minimum desired for operation, the thermal by-pass valve 40 will be positioned by its thermal element to connect the conduit 60 from the directional flow control valve 50 to both lines 38 and 39. In the following description of the operation, it is to be assumed that the selector switch 65 will be placed in the open position denoted as AUTO for automatic startstop operation as well as automatic free-unloading. As will be apparent from the electrical circuit of FIGURE 2,

placing the selector switch 65 in the closed position denited CONT. RUN will eliminate the automatic startstop features of the system but not the free-unloading operation.

Initial starting of the compressor system is preceded by closing the disconnect switch 61 which will energize the control circuit transformer 62 and the control circuit connected thereto and also connect the contactor-s of the compressor motor 11 and the blower motor 37 to the power source. Subsequent to closing of the disconnect switch 61, the start switch 63 is momentarily depressedto complete the starting circuit as has been previously described in detail and cause relay contacts 3CR1 to close. While the compressor motor 11 will be immediately started, the blower motor 37 will not start until the temperature of the oil in the system has risen to a desired maximum, 110 F. for example, causing switch TI-Il to close. A subsequent decrease in the oil temperature to a predetermined value, such as 100 F., will cause switch THl to open and the temperature of the oil will thus be maintained within the desired limits through continued operation of switch THI.

.Simultaneously with starting of the compressor motor 11, the directional flow control valve 50 will be actuated to place the system in loaded operation. The control valve S2 is not actuated at this time and conduit 53,

which'is connected through valve S2 and conduits 45 and 48 to the air service conduit 25, will therefore carry this pressure. The exhaust valve S3 interposed in conduit 53, since its solenoid will be energized simultaneously with starting of the compressor motor 11, will be operated to open conduit 53 to the air actuator 50b of the valve 50 and thereby pressurize this actuator. The other exhaust valve S4 will also be simultaneously operated to connect conduit 44 to the air actuator 5012. As the air actuator 50a will be vented to the atmosphere through conduit 44 and the exhaust port of valve S2, the pressurized actuator 5% will cause the spool of valve 50 to shift and thus provide the indicated porting arrangement. It will be noted that the check valve 51 is installed in conduit 44 to permit free flow from the actuator 50a and the valve 50 will be quickly shifted to the loaded position thereby permitting the compressor 10 to immediately take up the load.

With the valve 50 thus shifted to the loaded position, conduit 54 will continue to be blocked and the compres sor 10 will necessarily pump into the air receiver 21 through conduit 20. Conduits 56 and 59 will be connected forming a closed path from the oil outlet to the inlet of the cyclone separator 57. The conduit leading from the oil tank 23 will be connected to conduit 60 completing the oil supply circuit through the thermal bypass valve 40.

Since the pressure in the air service conduit 25 at the time of initially starting will be below the minimum opera tional pressure, which may be p.s.i.g., switch PS will be maintained in its first position energizing the solenoid of the valve S1. When thus energized, valve S1 will be open, permitting the separated oil to flow from the separator 24 through conduit 27 and into the interstage manifold 14, along with any air that may be mixed therewith. Continued operation will permit the oil pump 30 to induce an oil flow through conduit 31 into the oil gallery 32 of the compressor 10. After establishment of a minimal oil flow, the flow switch FLS will be actuated closing its contacts and thus by-pass contacts 1T R1. The contacts 1TR1 will remain by-passed as long as oil is flowing through conduit 31 for proper cooling and lubrication of the compressor 10. Simultaneously with starting the compressor, 10, the operating coil lTR of the time .delay relay will be energized and Will open its associated contacts 1TR1 after a predetermined time interval of, for example, five to ten seconds. the contacts 1TR1 places continued operation of the compressor system under control of the flow switch FLS. At any subsequent time, should the oil flow from the pump 30 be insuflicient for cooling and lubrication, the flow switch FLS will open to deenergize relay coil 2TR. After a predetermined time interval, five seconds for example, contacts 2TR1 will open causing contacts 3CR1 to open and thus disconnect the remainder of the control circuit from the transformer 62. Should there be an interruption in the oil flow through conduit 31 of momentary duration at any subsequent time, the time delay relay coil ZTR and its associated contact 2TR1 will prevent stopping of the compressor 10. If the interruption of oil flow should be prolonged, more than 5 seconds, the contact 2TR1 will open to stop the compressor and thereby prevent damage. This relay will elfect a deenergization of the complete control circuit necessitating manual operation of the start switch 63 for a subsequent restart. It will be apparent that this delay relay is a safety device which will require the operator to make the necessary repairs or adjustments before operation of the compressor may be continued.

, Assuming that the compressor 10 and its oil pump 30 are operating normally, air will be drawn through the air intake filter 17 and the open .unloader valve 16 into the low-pressure stage 12 of the compressor during a loaded operational cycle. The air will be compressed and discharged through the conduit 20 into the air receiver 21 and other connected tanks and conduits .to build up the-compressed air supply. The contacts of the pressure Opening of i sumption. I

' surernay'be approximately 105 p.s.i.g., as inthe usual tinued supply of compressed air. A loaded operational cycle will continueas long as there-is a continued demandfor compressed air and the pressure in the air 1 service conduit 25 does not reach the maximum operating pressure which may be about 105 p.s.i.g.

When the compressed air requirements have been fully 'met, or the capacity of the compressor is suchthatthe' output thereof exceeds the current air requirements, the

compressor 'systemof this invention Will automatically revert to free-unloaded operation tominirnize power con- Where the maximum desired operational prescompressed air systems, the pressure switch PS is set to be actuated'at this maximum pressure andthe pole thereof will be switched to the second position to energize the solenoidof valve S2. Simultaneously, the solenoid of valve S1 will be deenergized and this springbiased valve 'Wlll be closed,preventing further how of separated oilfrom the separator 24-. Energizationof the solenoidof valve 82- causes displacement of the movi able member thereof to connectthe oonduitsdl i and 41 'to conduit 45. Pressurization of the air pilot actuator of the unloader valve 16 is thus effected as-the pressure in conduit 41 will be that of the air service conduit 25' to which conduit 45 is connected and the air may flow freely through. the check valve 42 into the air pilot actuator of V l2. This represents a time lag which; is undesirable and which is eliminated by this system. Assuming that the tanks were pressurized prior to the unloaded operation or the compressor 18 Wasstopped, returnof the compressor to loaded operation will be accompanied by an al-. most immediate assumption of the compressed air load as only conduit and the portion of conduit Ztl between the high-pressure stage 13 andtheicheck valve 22 will require pressurization. l

Free-unloading operation of thecompress'or it, with the unloader valv'e, ldclosedand the. high-pressure side of the compressor openedto the; atmosphere through the valve Silyseparator 57 and exhaust silencer 58 will conthe unloader valve-16. The unloader valve 16 will thus be closed preventing further flow. of air into the lowpressure stage 12.

Conduit E l-"being connected to the pressurized conduit 45 will also pressurize the air actuator 5600f valve d through the exhaust valve S4 which remains energized.

The exhaust valve S3 also remains energized and the .air 1 t actuator 55% will be vented, to .the atmosphere through the-exhaust port'of the control valve 82.- which is now connested to conduit 53. Pressurization of the air actuator tard the flow. The delay is desirable to assure that the unloader valve in will be closed before the remainder of the system isreconnected by the directional flow control I v valve 5d.

In the unloaded position, conduit 54'is connected to conduit 59'and the high-pressure stage 13 of the compressor-Will discharge into the cyclone separator 57. During unloaded operation, the air-oil mixture discharged from the compressor is predeterminantly oil as there isvery little air that enters the compressor, only -the air coining from the scavenging system conduit 18,-and the separator 57 must have an adequate capacity rating for the unloaded operation. The oil flow'through the compressor remains substantially the same for either loaded or un loaded operation; Air separated from the compressor discharge will be vented to'the atmosphere through the exhaust silencer 58. Oil separatedby the separator 57 is returned'to the system'through the conduit 56 which is now connected to conduit as through the vaive 5t tinue until the pressure in the air service conduit 25 has droppedto the minimal operating pressure of approximately 90 p.s.i.g.. At this pressure, the switch PS Will be reset to itsfirst position for further loaded operation, as previously described. Valve' S1 -W lll accordingly be actuated byenergization of its solenoid to' open conduit 27 and the control valve S2 will return to its normal position as its solenoid will be deenergizedw Conduit 44 Will again be vented to the atmosphere through valve -S2 and conduit 53 will be pressurized again as it will be connected to conduit through valve 52. The pressurized air Within the actuating cylinder of the \unloader-valve'it will exhaust through the restricted' by-pass 43 and conduit 41 to the atmosphere. The restricted by-pass 43 preventsinstantaneous operation of the 'unloader valve 16 for protection of: the valve and the compressor 11' Air actuator Sil'bis also pressurized again and Will shift the spool of valve 5tlto the loaded position as air actuator a is now vented to the atmosphere through conduit 44, check valve 51 and the exhaust port ofthe con- 7 trol valve 82. The directional flow control valve 50 thus connects the several conduits of the system as previously described for operation of the compressor in a loaded state. a t

During this free-unloaded operation of the oompressor,-the scavenging system comprising thejet'produced by the conduit 18, as previously described, and directed into the manifold 14, Will function to prevent accumulation of oil in the manifold.

An automatic starting and stopping circuit is also incorporated in the compressor system, .as previously indicated, During free-unloaded operation, the operating coilfiTR of the third time. delay. relay will be energized simultaneously with the solenoid of valve .52. This time of contacts 3TR1, the operating coils lCR and 20R of The oil supply conduit 55 leading from the oil tank 23,

is blocked by the porting arrangement of the directional flow control valve 5i) and completes the isolation of the compressed air receiver system.- The'oil bleeder pipe 27. v

the'motor coutactors will-be deenergizedr-and thereby disconnect the; motors H'and 37- from the power sup- .ply'lines L1,; L2 and L3. The operating coil lTR of the first time delay relaylwill also .b'e'deenergized 'at the expiration of this timing interval; Contacts. lTRll will instantaneously close andthe flow switch .FLS Will subsequently open when the oil flow through conduit 31 has sutliciently decreased. The operating cbilZTR- of the second time' delay relay will, thus remain energized and maintain the associated contact ZTRIl closed which in is blocked by the closed valve S1 .and eonduit/Ztlds J I blocked by the chcckyalve 2 2. With'this system, the pre vio usly compressedairin the several tanlts Will not be lost when the compressor it is fully; unloaded for tree-unloaded. operation as in accordance I with this in- These: tanks are necessarily of a correspond .turn maintains relay 36R energized: The contact SGRl of thisrelay will remain clos'edjto permita subsequent restart of the compressor motor 11.; j

' Simultaneously .fWl'tll the. deenergization of L operating coils ICR, ZCR .anddTlL-l thefiolenoidsof the exhaust valves S3 and S4 will-be ,deenergized. The porting of each valve is such that, when the solenoid 'isi deenergized,

the air actuators Stla andfitlb willsbeventedto the-atmosphere through, an exhaust port or, the respective. valve- S4 and S35. Qonduit ldiwhich is pressurized at this time through the control valve S2, is blocked by the exhaust valve S4 to maintain pressure. Removing air pressure from the air actuator 50a through the exhaust valve S4. when stopping the compressor as a result of operation of delay relay STR permits the flow control valve 50 to center. The air actuator 50b is vented to the atmosphere through an exhaust port of the exhaust valve S3. Since the directional flow control valve 50 is spring centered and both air actuators are open to the atmosphere, the spool of the valve will be returned to the center position with all ports blocked. In its center position, the flow control'valve 50 will prevent further fluid flow in the system, such as a reverse flow of oil through conduit 60, and will require a minimum of time to be shifted to its loaded position for a subsequent operating cycle.

The exhaust valves S3 and S4 are of particular advantage in the stopping of the compressor 10, whether a normal stop as has been described or an emergency stop. In either case, it is desirable to have the directional flow control valve 50 return to its center position as soon as possible. All ports of the valve 50 will be blocked in the center position to prevent further fluid flow, either oil or air or a mixture, in the system. Regardless of whether the compressor system is operating in a loaded or unloaded cycle, the valve 50 will be permitted to return instantly to its center position.

At any subsequent time that the pressure in the air service conduit 25 decreases to 90 p.s.i.g., switch PS will be reset, deenergizing the solenoid of valve S2 and the operating coil 3TR of the time delay relay and energizing the solenoid of valve S1. Contacts 3TR1 of this relay will be instantaneously closed to reconnect coils lCR, ZCR and 1TR and the solenoids of the exhaust valves S3 and S4 into the circuit. The compressor motor 11 and blower motor 37 will thus be restarted, as previously described, in conjunction with the initial starting phase.

It will be apparent from the above that our invention provides in an internally oil-cooled, positive displacement type rotary compressor, means for greatly reducing the power required to run the compressor in an unloaded state, that is, when it is not pumping a substantial volume of fluid at an elevated pressure. The unloading of the intake side of the compressor is accomplished at the intake valve whereas the unloading of the receiver or high-pressure discharge side of the compressor is accomplished by venting the air therefrom through an oil separator where the oil is removed from the air and the oil is returned to the system while the air is to be exhausted to the atmosphere without a loss of circulating oil. Unloading of the high-pressure discharge side of the compressor in this manner prevents loss of compressed .air from the receiver system tanks to permit immediate assumption of the load by the compressor upon restart or return to loaded operation from unloaded operation. Thus, the power to drive the rotors during the unloaded state of the compressor is greatly reduced. Furthermore,

this invention provides oil scavenging means which functions in association with the unloading system for preventing the accumulation of oil in the interstage manilfold which otherwise might cause damage to the rotors.

vtank so that the separate oil tank could be eliminated. Also, the oil separator tank could be disposed within the receiver tank. Our free unloading system and the associated oil scavenging system would work equally as iwell with such modifications of the compressor system.

According to the provisions of the patent statutes, the

principles of this invention have been explained and have been illustrated and described in what is now considered to represent the best embodiment. However, it is to be understood that, Within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

Having thus described this invention, what we claim is:

1. A rotary compressor comprising low-pressure and high-pressure stages having air-compressing rotors, a pressure lubricating-cooling system for said stages and connected thereto, an inlet valve connected to said lowpressure stage for controlling the inlet of air thereto, an air and oil receiver system connected to a discharge port of said high-pressure stage for receiving the air and oil mixture discharged therefrom and including a service conduit leading therefrom, said receiver system being connected to said discharge port by a conduit having a check valve interposed therein to prevent fluid flow from said receiver system, a directional flow control valve connected to said discharge port to vent said highpressure stage to atmosphere, and control means connected to said valves for closing the inlet valve and operating the flow control valve to vent said high-pressure stage for freely unloading the compressor, said control means being responsive to the pressure in said air service conduit for actuation to close said inlet valve and operating the flow control valve to vent said highpressure stage when the pressure in said service conduit reaches a selected upper limit to thereby freely unload the compressor while maintaining said receiver system under pressure and to open said inlet valve and operate said flow control valve to prevent venting of said high pressure stage when the pressure in said service conduit reaches a selected lower limit to thereby load the compressor, said pressure lubricating-cooling system includ ing a supply tank connected in said receiver system and an air-oil separator vented to atmosphere, said supply tank and air-oil separator being connected to said flow control valve whereby actuation thereof to a first position will operatively connected said supply tank in said lubricating-cooling system and actuation to a second position will operatively connect the separator to the discharge port of said high-pressure stage, said valve when in said second position also preventing further outflow from said supply tank.

2. A rotary compressor comprising low-pressure and high-pressure stages having air-compressing rotors, a pressure lubricating-cooling system for said stages and connected thereto, an inlet valve connected to said lowpressure stage for controlling the inlet of air thereto, an air and oil receiver system connected to a discharge port of said high-pressure stage for receiving the air and oil mixture discharged therefrom and including a service conduit leading therefrom, said receiver system being connected to said discharge port by a conduit having a check valve interposed therein to prevent fluid flow from said receiver system, a directional flow control valve connected to said discharge port to vent said high-pressure stage to atmosphere, and control means connected to said valves for closing the inlet valve and operating the fiow control valve to vent said high-pressure stage for freely unloading the compressor, said control means being responsive to the pressure in said air service conduit for actuation to close said inlet valve and operating the flow control valve to vent said high-pressure stage when the pressure in said service conduit reaches a selected upper limit to thereby freely unload the compressor while maintaining said receiver system under pressure and to open said inlet valve and operate said flow control valve to prevent venting of said high-pressure said air and oil mixture receiver system including an airoil separator, a conduit connecting the separator with said pressure lubricating-cooling system at a point which is substantially lower in pressure, and a two-way valve is, interposed in said conduit and operatively connected to said control. means, said valve having a first. position wherein said conduitis blocked and a second position permitting fluid flow through said conduit.

3. A rotary compressor according'to claim 2 in Which said low and high-pressure stages are connected by an interstage'manifold and said conduit leading from said receiver system is connected to said manifold. I

4. A rotary compressor comprising low-pressureand high-pressure stages having air compressing rotors, apressure lubricating cooling system for said stages and connected thereto, an inlet valve connected to said low'pressure stage for controlling the inlet of air thereto, an air and oil receiver system connected to a discharge port of said high-pressure stage for receiving the air and oil mixture discharged therefrom and including a'service conduit leading therefrom, said receiver system being connected to said 'dislcharge port by a conduit having a check valve interposed therein to preventfluid flow from said receiver system, a directional flow control valve'connected to said discharge port to vent said high-pressure stage to atmosphere, and control means connected to said valves for closing the inlet valve and operating the'flow control valve'to vent said high-pressure stage for freely unloading the compressor, said control means being responsive to the pressure in said air service conduit for actuation to close said inlet valve and operating the flow control valve to vent said high-pressure stage when the pressure insaid service conduit reaches a selected upper limit tothereby freely unload the compressor while maintaining said receiver system under pressure and to open said inlet valve and operate said flow control valve to prevent venting of said high-pressure stage when thepre'ssure in'said service conduit reaches a selected lower limit to thereby load the compressor, said inlet valve and saidtfiow control valve being air-actuated, and said control means including a i6 v being operative to start said rotor drive motor when the pressure in said air service conduit reaches said selected lower limit and to stop said rotor drive motor when the pressure in said air service conduit reaches and is maintained at said selected upper limit fora predetermined time interval. I I I 7 6. A rotary compressor according tofclairn 5 wherein said control apparatus includes timing means connected therein for ascertaining said "predetermined time interval. 7. A rotary compressor according to claim 6 wherein said pressure lubricating cooling system includesa heat exchanger of the forcedtcirculation type'having a drive motor and said control apparatus is operative for selectively starting and stopping said' heat exchanger drive motor. 7

SJA'r'otary compressor comprising low-pressure and high-pressure stages having air-compressingrotors, a pressure lubricating-cooling system for said stages and connected thereto, an inlet valve. connected to said lowpressure stage for controlling the inlet ofair thereto, an air and oil receiver system connected to a discharge port of said high-pressure stage for receiving the air and oil mixture discharged therefrom and including a service conduit leading therefrom, said receiver system beingconnected to said dischargeport by a conduit having a check valveinterposed therein to prevent fluid flow from said receiver system, a directional flow control valve connected 7 to "said discharge port to vent said high-pressure stage to control valve having an electromagnetic solenoid for the actuation thereof, a conduit interconnecting said inlet valve and said flow, control valve through said control valve to a source of pressurized air, and an electric circuit having a p ower source and switch means connected in circuit withsaid control'valve solenoid, said switch means being of the pressure-actuated type having a pressure responsive element which is pneumatically connected to of said .high-pressurerstage for receiving the air and oil.

mixture discharged therefrom and including a service conduit leading therefrom, said receiversystem being con- 7 nected to said discharge port by a conduithaving a check valve interposed therein to prevent fluid flow fromsaid 'receiversystem, a directional flow control valve connected to said discharge port to ventsa'id high-pressure stage to atmosphere, and control means. connected to said'valves for closing the'inlet valve and operating the flow control val ve to .vent ,said high-pressure stage forfreely unloading the compressor, said control means being responsive to the pressure in said air service conduit for'actuation to close said inlet valve and, operatingthe flow control valve to vent" said high-pressure stage when the pressure in said service conduit reaches aselectedupper limit totherehy freely, unload the compressor while maintaining said receiver system under pressure and to open said inlet valve and operate said flow control valve to prevent venting of 'said high-pressure stage when the pressure in said servicev 'conduit'reachesa selected :lower limit'to thereby load the compressor, said' air compressing rotors being coupledtto a a drive motor'for the operation thereof and said'control means including control apparatus forselectively starting a or stopping said rotor drive motor, said control apparatus freely unload thecompressor whilermaintaining said receiver system underpressure and to open said inlet valve and operate said flow control valve toprevent venting of said high-pressure stage when the pressure in said service conduit reaches a selected lower limit to thereby load the compressor, 'said low and high-pressure stages being con-- nected by an interstagemanifold and including means for scavenging oil from said manifold during unloaded operation, said means comprising a fluid conduit connected to said manifold at the upstream end thereof and connected 7 to a source of'fluid under greater pressure than that in the manifold during unloaded operation of the compres-v sor.

91A rotary compressor comprising high-pressure, stages having air-compressing:'rotors, a pressure, lubricating-coiling system for said stages and connected'thereto, an inlet valve connected to said lowvpressure lubricating cooling system for :said'stages and air and oilreceiver system 'connected to adischarge port of said high-pressure stage for receiving the airand oil a. mixture discharged therefrom and including a service conduit leadingtherefrom, said receiver system being connected to said discharge :port by a conduit having a check valve interposed therein to prevent fluid flow from said receiver systen1 ,:a vdirectional flow :control valve 'coni nectedto said discharge port to vent said'high-pr'essure stage to atmosphere, and control means connected to said valves for closing the inlet valve :and operating the flow control valve "to rventxsaid high-pressure stage for freely unloading .theucompressorgsaid control means being, responsive to the ,m ssuretin said air: service conduitufor actuation to .close saidinletiva'lve and operating the flow control valveitovent said highpressurestage'VWhen the pressurelin said service conduit reaches a selected upper limit to 'tl ierebyfreely unload the compressor while maintaining said; receiver system under-pressure and to' open a said inlet valve'and'operate said flowfoontrol' valve to prevent venting of saidghighfpressure'stage when the pressu re' {inj'saidserviceconduit reaches a selected low limit tov "thereby load tlie compressor, said low and'high-pressure' I low-pressure and stages being connected by an interstage manifold and including means for scavenging oil from said manifold during unloaded operation, said means comprising a fluid conduit connected at one end to the upstream end of said manifold and open at the opposite end to the atmosphere, said fluid conduit having a check valve interposed therein to prevent fluid flow therethrough from said manifold during loaded operation of the compressor.

it A rotary compressor comprising interconnected low-pressure and high-pressure stages having air-compressing rotors, a drive motor coupled to said rotors, an inlet valve connected to said low-pressure stage for controlling the inlet of air thereto, an air and oil receiver system connected to a discharge port of said high-pressure stage for receiving the air and oil mixture discharged therefrom and including an air-oil separator, an air service conduit connected to said receiver system, a conduit interconnecting said receiver system with said high-pressure stage having a check valve interposed therein to prevent fluid flow from said receiver system to said highpressure stage, an oil bleeder conduit connected to said air-oil separator for removal of oil separated therefrom and including means for restricting the outflow of fluid, a two-way valve interposed in said oil bleeder conduit and operative to block said conduit in a first position and permit fluid flow through said conduit in a second position, means for actuating said two-way valve, a pressure lubricating-cooling system for said stages and connected thereto including an oil supply tank communicating with said receiver system for accumulating oil received by said receiver system during loaded operation of the compressor, a second air-oil separator vented to the atmosphere, and an oil supply conduit connected to said stages, a directional flow control valve connected to said oil supply tank, said second air-oil separator, said oil supply conduit and the discharge port of said highpressure stage between said discharge port and the check valve in the conduit connecting with said receiver system for selectively controlling the flow of the air and oil mixture discharged from said high-pressure stage and to control the flow of oil in said pressure lubricating-cooling system, and control means connected to said inlet valve, said directional flow control valve and the actuating means of said two-way valve for closing the inlet valve, operating the flow control valve to vent said high-pressure stage while maintaining a flow of oil through said lubrieating-cooling system and closing said two way valve to block the bleeder conduit for maintaining said receiver system under pressure, said control means being responsive to the pressure in said air service conduit to close said inlet valve, operate said flow control valve to vent said high-pressure stage and to cause said two-way valve to close when the pressure in said air service conduit reaches a selected upper limit to thereby freely unload the compressor while maintaining said receiver system under pressure and to open said inlet valve, operate said flow control valve to prevent venting of said high-pres sure stage and to cause said two-way valve to open when the pressure in said service conduit reaches a selected lower limit to thereby load the compressor.

11. A rotary compressor according to claim It} wherein said directional flow control valve is of the three-position type having a first position in which flow of oil in said lubricating-cooling system is prevented and said highpressure stage is not vented, a second position in which said high-pressure stage is not vented and said oil supply tank is connected in said lubricating-cooling system and a third position in which said high-pressure stage is vented to atmosphere through said second air-oil separator, said second oil separator is connected in said lubricating-cooling system and further flow of oil from said oil supply tank is prevented.

are air-actuated and said two-way valve is actuated by an electro-magnetic solenoid, and said control means includes a control air valve having an electromagnetic actuating solenoid, a conduit interconnecting said inlet valve actuator and said flow control valve actuator through said control valve to a source of pressurized air, and an electric circuit having a power source and switch means connected in circuit with said control valve solenoid and said two-way valve solenoid, said switch means being of the pressure-actuated type having a pressure-responsive element which is pneumatically connected to said air service conduit for actuation of said switch means in accordance with the pressures in said service conduit.

13. A rotary compressor having afluid inlet system and a fluid receiver system with fluid-compressing means connected therebetween, a pressure lubricating-cooling system for said compressing means and connected thereto,

an inlet valve forming part of said inlet system for controlling the inlet of air to said compressing means, said receiver system being connected to a discharge port of said compressing means for receiving air and oil mixture discharged therefrom and including a service conduit leading therefrom, said receiver system being connected to said discharge port by a conduit having a check valve interposed therein to prevent fluid flow from said receiver system, a directional flow control valve connected to said discharge port to vent said compressing means to atmosphere, and control means connected to said valves for closing the inlet valve and operating the flow control valve to vent said compressing means for freely unloading the compressor, said control means being responsive to the pressure in said air service conduit for actuation to close said inlet valve and operating the flow control valve to vent said compressing means when the pressure in said service conduit reaches a selected upper limit to thereby freely unload the compressor while maintaining said receiver system under pressure and to open said inlet valve and operate said flow control valve to prevent venting of said compressing means when the pressure in said service conduit reaches a selected lower limit to thereby load the compressor, said pressure lubricating-cooling systemincluding a supply tank connected in said re ceiver system and an air-oil separator vented to atmosphere, said supply tank and air-oil separator being connected to said flow control valve whereby actuation thereof to a first position will operatively connect said supply tank in said lubricating-cooling system and actuation to a second position will operatively connect the separator to the discharge port of said compressing means, said valve when in said second position also preventing further outflow from said supply tank.

14. A rotary compressor having a fluid inlet system and a fluid receiver system with fluid-compressing means connected therebetween, a pressure lubricating-cooling system for said compressing means and connected thereto, an inlet valve forming part of said inlet system for controlling the inlet of air to said compressing means, said receiver system being connected to a discharge port of said compressing means for receiving air and oil mixture discharged therefrom by a conduit having a check valve interposed therein to prevent fluid flow from said receiver system when the compressing means is loaded, a directional flow control valve connected to said discharge port of said compressing means, said pressure-lubricating cooling system including an air-oil separator having an inlet connected to said flow valve and having an air outlet connected to atmosphere and an oil outlet connected to said flow valve, said receiver system also including oil- 12. A rotary compressor according to claim it in which said inlet valve and said directional flow control valve accumulating means having an oil outlet line connected to said flow valve, said pressure lubricating-cooling system also including an oil inlet line leading from said flow valve to said compressing means which connects with said oil outlet line through said flow valve when the compressing means is loaded, and control means connected to means oil outlet line to prevent flow offiuid from the receiv'er. system.

15. A compressor according to claim 14 in which said receiver system also includes an air-oil separator, a bleed 7 line leading from said last-named separator to said com-t pressing, means, and a control valve in said bleed line connected to said control means and actuated thereby in response to said predetermined receiver pressure to block said, line,

;16.{A rotary compressor having a fluid inlet system anda fluid receiver system with fluid-compressing means connected therebetween, a pressure lubricating-cooling systernfor said compressing means and connected thereto,

inlet valve means forming part of said inlet system for controlling the inlet of air to said compressing means, said receiver system being connected to a discharge port of said compressing means for receiving air and oil mixture discharged therefrom when said compressing means is loaded, directional flowcontrol valve means connected to'said discharge port of said compressing means, said pressure-lubricating cooling system also including an oil inlet line leading from said flow control valve means to 7 said compressing means which connects with said oil outlet line through said flow valve when the compressing m ans is loaded, and control means connected to said valve means and to said receiver system and responsive to a predetermined pressure in said receiver system to close the inlet valve means to unload the compressing means and to operate the flow control valve means to connect said discharge port of the compressing means to said inlet of the separator and to connect said oil outlet of the separator to said'oil inlet line and also to block said accumulating means oil outlet line to prevent fiow of fluid from the receiverrsystem.

17. A rotary compressor having a fluid inlet system and a'fluid receiver system With fluid-compressing means connected therebetween and having a discharge outlet, a pressure lubricating-cooling system for said compressing means and connected thereto, inlet valve means forming part of-said inlet system for controlling the inlet of air to said compressing means, said receiver system being connected to the discharge outlet of said compressing meansfor receiving an and oil mixture discharged therefrom when the compressing means is loaded, directional flow control valve means connected to said compressing means discharge outlet and to an exhaust outlet but interrupting communication therebetween When the compressing means is loaded, said receiver system having an oil outlet connected to said control valve means, said pressure-lubricating cooling system also including an oil inlet leading from said'flow control valve means to said compressing means, which communicates with said oil out let through said valve means when the compressing means is L loaded, and control means connected to said valve means andre'sponsive to a predetermined pressure in said receiver system to close the inlet valve means to unload the compressing means and to operate the fiow control valve means to connect said discharge outlet of the compressing means to said exhaust outlet and to block said oil outlet to prevent flow of fluid from the receiver system.

18. A rotary compressor having a'fiuid inlet system and a fluid receiver system Withfluid-com'pressing means connected therebetween' and having a discharge outlet, a pressure lubricating-cooling system-for said compressing means and connected thereto, said inlet system including unloading means for unloading thecompressing means, said receiver system comprising a first section connected to said discharge outlet throughja check valve for receiving the air and oil mixture discharged through said discharge outlet from said compressing, means 'while it is loaded and'a second section for receiving the air and oil mixture discharged through said outlet when the compressor is unloaded, said second section beingconnected to atmosphere, said pressure-lubricating. cooling system including an oil inlet line connected to said compressing means, said first receiver section having an oil return line and said second receiver section having an oil return line, fiow valve means connecting said oil return lined the first receiver section to said oil inlet line and disconnecting the oil return line of thessecond receiver section from said oil inlet line when the compressing means is loaded, and control means connected to said flow control valve means and to said unloading meansto operate both of said means upon receiver pressure reaching a predetermined'amount, said control means actuating said valve means to connect said discharge outletof the compressing means to said second receiver section and to disconnect said oil return line of said first receiver section from said on inlet line but to connect said oil return line of the second receiver section to said oil inlet line.

,19. A rotary compressor having a fluid inlet system and a fluid receiver system with fluid-compressing means connected therebetween and having a discharge outlet, a pressure lubricating-cooling system for said compressing means and connected thereto, said inlet system including unloading means 'for unloading the compressing means, said receiver system comprising a first. section for receivting the air and oil mixture discharged throughv said discharge ontlet from said compressing means while it is loaded and a second section for receiving the air and oil mixture discharged, through said outlet when thecompressing means is unloaded, said second section having venting means adapted to be connected to the discharge outlet of said compressing means, each of said receiver sections having oil collecting and return passages adapted to be connected to said compressing means,'valve means for normally disconnecting the return oil passage of the second receiver section from thecompressing means and for connecting the return oil passage of the first receiver section to the compressing means anddisconnecting said discharge outlet from said venting means, and control means responsive to receiver pressure for actuating said unloading means and actuating said valve means'to disconnect the return oil passage of the first receiver section from said compressing means and to connect the return oil passage of the second receiver section to said compressing means and also to connect the discharge outlet of the compressing means to said venting means.

References. Cited by the Examiner UNITED STATES "PATENTS 1,855,675 4/32 Hansen 230-46 1,864,132 /32 Halleck 23 0 26 2,787,411 4/57 Hughes 230-26 X 2,895,665 7 59 McSweeney t 230-26 X ROBERT M. WALKER, Primary Examiner,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,186,631 June 1, 1965 Ralph E. Lamberton et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 7, lines 15 and 16, for "air-inspiring" read airinspirating column 11, line 52, for "predeterminantly" read predominately column 13, line 66, for "received" read receiver column 16, line 51, for "lubricating-coiling" r :ad lubricating-cooling line 53, strike out "lubricatingc' cling system for said stages and" and insert instead stage fcr controlling the inlet of air thereto, an line 74, for "low" read lower column 20, line 18, after "flow" insert control Signed and sealed this 21st day of December 1965.

EST W. SWIDER EDWARD J. BRENNER ing Officer Commissioner of Patents 

1. A ROTARY COMPRESSOR COMPRISING LOW-PRESSURE AND HIGH-PRESSURE HAVING AIR-COMPRESSING ROTORS, A PRESSURE LUBRICATING-COOLING SYSTEM FOR SAID STAGES AND CONNECTED THERETO, AN INLET VALVE CONNECTED TO SAID LOW PRESSURE STAGE FOR CONTROLLING THE INLET OF AIR THERETO AN AIR AND OIL RECEIVER SYSTEM CONNECTED TO A DISCHARGE PORT OF SAID HIGH-PRESSURE STAGE FOR RECEIVING THE AIR AND OIL MIXTURE DISCHARGED THEREFROM AND INCLUDING A SERVICE CONDUIT LEADING THEREFROM SAID RECEIVER SYSTEM BEING CONNECTED TO SAID DISCHARGE PORT BY A CONDUIT HAVING A CHECK VALVE INTERPOSED THEREIN TO PREVENT FLUID FLOW RFOM SAID RECEIVER SYSTEM, A DIRECTIONAL FLOW CONTROL VALVE CONNECTED TO SAID DISCHARGE PORT TO VENT SAID HIGHPRESSURE STAGE TO ATMOSPHERE, AND CONTROL MEANS CONNECTED TO SAID VALVES FOR CLOSING THE INLET VALVE AND OPERATING THE FLOW CONTROL VALVE TO VENT SAID HIGH-PRESSURE STAGE FOR FREELY INLOADING THE COMPRESSOR, SAID CONTROL MEANS BEING RESPONSIVE TO THE PRESSURE IN SAID AIR SERVICE CONDUIT FOR ACTUATION TO CLOSE SAID INLET VALVE AND OPERATING THE FLOW CONTROL VALVE TO VENT SAID HIGHPRESSURE STAGE WHEN THE PRESSURE IN SAID SERVICE CONDUIT REACHES A SELECTED UPPER LIMIT TO THEREBY FREELY UNLOAD THE COMPRESSOR WHILE MAINTAINING SAID RECEIVER SYSTEM UNDER PRESSURE AND TO OPEN SAID INLET VALVE AND OPERATE SAID FLOW CONTROL VALVE TO PREVENT VENTING OF SAID HIGHPRESSURE STAGE WHEN THE PRESSURE IN SAID SERVICE CONDUIT REACHES A SELECTED LOWER LIMIT TO THEREBY LOAD THE COMPRESSOR, SAID PRESSURE LUBRICATING-COOLING SYSTEM INCLUDING A SUPPLY TANK CONNECTED IN SAID RECEIVER SYSTEM AND AN AIR-OIL SEPARATOR VENTED TO ATMOSPHERE, SAID SUPPLY TANK AND AIR-OIL SEPARATOR BEING CONNECTED TO SAID FLOW CONTROL VALVE WHEREBY ACTUATION THEREOF TO A FIRST POSITION WILL OPERATIVELY CONNECTED SAID SUPPLY TANK IN SAID LUBRICATING-COOLING SYSTEM AND ACTUATION TO A SECOND POSITION WILL OPERATIVELY CONNECT THE SEPARATOR TO THE DISCHARGE PORT OF SAID HIGH-PRESSURE STAGE, SAID VALVE WHEN IN SAID SECOND POSITION ALSO PREVENTING FURTHER OUTFLOW FROM SAID SUPPLY TANK. 